1. Field of the Invention
The present invention relates to polycarbonate compositions and to their preparation and use, wherein the polycarbonate compositions contain an adsorber or absorber and an acid.
2. Description of Related Art
The present invention relates further to a compounding process for the preparation of stabilised polycarbonate compositions containing constituents having a basic action, using acids applied to an adsorber or absorber. The application of the acid to the adsorber or absorber is carried out, for example and preferably, by blending the adsorber or absorber with an acid that wets the adsorber or absorber or alternatively with a solution of an acid that wets the adsorber or absorber. In a preferred embodiment, these blends are pulverulent and pourable.
The compositions according to the invention, or prepared by the compounding process according to the invention, have improved processing stability, in particular improved stability of the gloss level with variation of the processing temperature, as well as increased heat stability and a good natural colour.
In the processing of polymers, compounding refers to the preparation of a finished plastics moulding composition, the compound, from optionally a plurality of polymeric raw materials with the optional addition of polymer additives such as, for example, fillers and reinforcing materials, adhesion promoters, lubricants, stabilisers, etc. Compounding takes place, for example, in kneaders or extruders and comprises the process operations of feeding, melting, dispersing, mixing, degassing and pressure build-up. Compounding is generally followed by solidification of the compound, which is effected by cooling, and granulation thereof.
Impact modifiers, which are used in the preparation/compounding of polycarbonate compositions, often contain basic impurities as a result of their preparation. They contain, for example, residual amounts of substances having a basic action, which are used as polymerisation aids, for example as emulsifiers in emulsion polymerisation, or as auxiliary substances in the working-up processes. In some cases, additives having a basic action (e.g. lubricants and demoulding agents) are also added purposively to ABS polymers. Likewise, many commercially available fillers, such as, for example, talc or other commercially available polymer additives such as, for example, some antistatics (for example polyether amides), lubricants (for example ethylene bis stearamide), stabilisers (for example benzotriazoles used as light stabilisers), pigments (for example titanium dioxide), nitrogen-containing organic colourings (for example azo compounds or pyrazolones) and nitrogen-containing flame retardants (for example phosphonate amines), exhibit alkaline behaviour or contain basic impurities.
Such additives or impurities having an alkaline action can cause catalytic decomposition of the polycarbonate at high temperatures such as typically occur in the preparation and processing of polycarbonate moulding compositions. Such polycarbonate degradation often manifests itself in a deterioration of the properties of the moulding compositions, in particular of the mechanical parameters such as ductility and tensile elongation properties, but also by molecular weight degradation and surface changes. As a result, the choice of possible substances for use for such polycarbonate compositions is very greatly limited.
While it is known from the prior art to add acidic compounds such as, for example, citric acid to polycarbonate compositions in order to neutralise the harmful effect of additives or impurities having an alkaline action, the addition of such acids frequently leads to disadvantageous properties in the polycarbonate compositions, such as, for example, streaking on the surface, pronounced molecular weight degradation and/or impairment of the natural colour.
EP-A 576 950 A1 and WO-A 2007/065579 describe compositions containing polycarbonate and acrylonitrile-butadiene-styrene (ABS) polymers, which compositions contain basic impurities and are stabilised with multifunctional organic carboxylic acids. Such compositions have good heat stability with regard to the integrity of the molecular weight of the polycarbonate component at high processing temperatures, but they tend to form surface defects (streaks) on the mouldings produced therefrom in injection moulding.
US2006/0287422 describes thermoplastic compositions containing polycarbonate, an impact modifier, optionally a vinyl copolymer, a mineral filler and an acid or an acidic salt, having improved mechanical properties and a reduced tendency to thermal degradation. The application discloses as preferred acids also phosphorus-based compounds of the general formula HmPtOn, specifically inter alia also phosphoric acid. The application discloses that the compositions according to the invention can be prepared by processes described in the prior art.
In WO-A 2010/063381 there are described impact-modified polycarbonate compositions having an improved combination of hydrolytic and processing stability, which compositions contain polycarbonate, an emulsion graft polymer containing basic impurities, and an acidic phosphorus compound having at least one P—OH functionality. As acidic phosphorus compounds there are described both specific cyclic organophosphite compounds and inorganic or organic phosphorus compounds such as, for example, phosphoric acid or phosphoric acid esters.
EP 2 257 590 A1 discloses polycarbonate compositions having an improved combination of natural colour, hydrolytic stability and processing stability, containing polycarbonate, rubber-modified graft polymer containing residues of a fatty acid salt emulsifier resulting from its preparation, wherein the graft polymer in aqueous dispersion has a pH value greater than 7, and an acidic additive. In this application, hydroxy-functionalised mono- and poly-carboxylic acids as well as phosphoric acid are disclosed as the acidic additive.
EP 1 141 107 A1 discloses polycarbonate compositions having improved heat distortion resistance, elongation at break and stress cracking resistance, containing polycarbonate, graft polymer, optionally vinyl copolymer and from 0.1 to 30 parts by weight of a silicon compound such as, for example, silicon dioxide having a mean particle diameter of from 3 to 50 nm. This application is silent regarding the use of acids in the compositions.
However, none of the mentioned passages describes the compositions of the present invention or the process for their preparation.